Low back pain is a frequent cause of disability and a common reason for outpatient care in veterans. Magnetic resonance imaging (MRI) of the lower back often reveals abnormalities,which may be used to justify expensive and invasive therapy, such as surgery. Yet the link between MRI abnormalities and the risk of developing clinically significant back pain is far from clear. This longitudinal study will determine the prevalence and incidence of MRI abnormalities among veterans and determine the extent to which specific MRI abnormalities predict future development of back pain. The result should help clinicians use MR imaging more efficiently, and they may ultimately help reduce the frequency of unnecessary back surgery.